fix 15, 16, 17, 18, 19 issue

[Nika-Soltani-Tehrani]

Fixes # by...

Changes proposed in this pull request:

• Changed the format of converting five numbers include (15, 16, 17, 18, 19)

Status

• READY
• HOLD
• WIP (Work-In-Progress)

How to verify this change

Fill out this section so that a reviewer can know how to verify your change.
By testing the num2words/lang_FA.py file and calling the 'cardinal3' function, when you should see the below result:

num2word_fa = Num2Word_FA()
number = int('۱۹')
modified_number = num2word_fa.cardinal3(number)
print(modified_number)
# result: نوزده

Before this change, the result was 'نه و ده' which is wrong.
Also for numbers ۱۵, ۱۶, ۱۷, ۱۸ it has to result in: 'هجده', 'هفده', 'شانزده', 'پانزده'

Additional notes

If applicable, explain the rationale behind your change.
This problem was a little but impactful mistake in using the formal Persian language, not the informal one.

[coveralls]

Coverage: 97.171% (+0.0005%) from 97.17% when pulling 77fbe91 on Nika-Soltani-Tehrani:fix-numbers-issue into 3ef32f0 on savoirfairelinux:master.